Method of cryogenic stretch blow molding

ABSTRACT

A method of stretch blow molding a plastic parison mounted to a parison engagement assembly into a container including stretching the parison by sliding the stretching rod therethrough and into the parison, connecting the cooling fluid inlet port to the source of cooling fluid to introduce the cooling fluid within the container through the cooling fluid outlet port, and heating the blow mold rod seal assembly to maintain at least a portion of the stretching rod above the preselected level, and to maintain portions of seals above the predetermined level.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 08/963,931 filed Oct. 31,1997, now U.S. Pat. No. 6,168,414.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the field of stretch blowmolding apparatus for producing plastic containers from parisons, andmore particularly concerns stretch blow molding methods and apparatusutilizing cryogenic fluids to cool plastic containers stretch blowmolded from parisons.

2. Description of the Prior Art

In biaxially stretch blow molding parisons into plastic containers, aparison may be placed within a blow mold cavity and mounted to a parisonengagement assembly, with a stretching rod moved into and along thelongitudinal axis of parison, stretching the parison longitudinally.Blow air is introduced into the parison, laterally stretching theparison transverse to the stretching rod. To provide such stretch blowmolded containers with heat resistant characteristics, permittingfilling with heated fluid, containers may be heat-set to favorablyadjust the orientation of the polymers. In order to shorten theoperational time required to heat-set stretch blow molded containers,cooling fluids may be introduced within the containers, quicklyquenching and heat-setting the container to permit rapid removal fromthe blow mold.

The introduction of cryogenic liquids through a stretching rod into theinterior of a container that has been stretch blow molded from a parisonis known in the art, for instance, as disclosed in U.S. Pat. No.5,182,122. Further, apparatus and method of making a partiallycrystalline container by stretch blow molding within a hot mold and theninjecting a cooling fluid within the blown container is also known, asdescribed in U.S. Pat. No. 4,883,631, and corresponding United Kingdompatent application No. 2,195,287. Introduction of liquid nitrogen withina container for purposes of cooling is disclosed in U.S. Pat. Nos.5,290,506; 4,375,947 and 4,376,009. The use of U.S. Pat. Nos. 5,290,506;4,375,947 and 4,376,009. The use of cryogenic gas is also known inextrusion blow molding, as described in U.S. Pat. No. 3,789,093.

Unfortunately, the use of cryogenic fluids with stretch blow moldingapparatus may also cause certain components of the apparatus to cool toa temperature where the apparatus becomes inoperative. In particular,cryogenic fluids may lower the temperature of components in contact withblow air to a level where water vapor present in the blow air sublimatesonto surfaces of such cryogenically cooled components, causing anaccumulation of water ice on the surfaces. With continued accumulationof water ice, the apparatus may be rendered inoperable. In addition,when the temperature of the sealing surfaces of seals present in astretch blow mold apparatus decreases below a certain level that ischaracteristic of the materials from which the seals are formed, theseals may fail catastrophically. As a result, there exists a need formethods and apparatus for preventing accumulation of water ice and sealfailure during stretch blow molding using cryogenic fluid.

U.S. Pat. No. 5,182,122 has proposed a solution to problems created byutilizing cryogenic fluids which includes using a stretching rod havingan inner tube for delivery of a cooling fluid and a concentric outertube for delivery of a thermally insulating fluid. Despite theavailability of such devices, there exist a need in the art for methodsand apparatus which permit the introduction of cryogenic fluid within astretch blow molded container for rapid cooling while preventingaccumulation of water ice and maintaining the integrity of the seals,but without the necessity of providing for delivery of a thermallyinsulating fluid.

SUMMARY OF THE INVENTION

In order to aid in the understanding of the present invention, it can bestated in essentially summary form that it is directed to methods andapparatus for stretch blow molding a parison into a container includingthe introduction of a cryogenic fluid within the container for rapidcooling and providing a source of heat to prevent the cryogenic fluidfrom causing accumulation of water ice and failure of seals.

More specifically, the present invention includes an apparatus forstretch blow molding a plastic parison into a container, for use with aparison engagement assembly for engaging a parison for stretch blowmolding within a blow mold. The apparatus includes a blow mold rod sealassembly having a thermally conducting blow manifold, a thermallyconductive blow seal housing, and a thermally conductive base platemounted to a top plate so that the blow seal housing is sandwichedbetween and in thermal contact with the blow manifold and the baseplate.

A blow manifold defines a first stage blow air inlet port for connectionto a source of blow air through a blow air fitting, and further definesa second stage blow air inlet port for connection to the source of blowair. The blow manifold also defines an interior cavity first portiondisposed in fluid connection with the first and second stage blow airinlet ports, a chamfered countersink communicating with the interiorcavity first portion, and a blow air outlet port.

The blow seal housing includes an upper end and a chamfered lower end,with dimensions of the lower end selected for the blow seal housing tobe disposed proximate to the blow manifold with the lower end in matingengagement with the countersink. The blow seal housing defines aninterior cavity second portion having a generally cylindrical smallerchamber and a coaxial generally cylindrical larger chamber separatedfrom the smaller chamber by a step. The blow seal housing furtherdefines a first low pressure air supply orifice, disposed through theblow seal housing and communicating with the interior cavity secondportion. With the blow seal housing engaged with the blow manifold, thesmaller chamber is disposed proximate to the interior cavity firstportion.

The base plate is disposed proximate to the blow seal housing anddefines an interior cavity third portion having a generally cylindricalfirst chamber and a generally cylindrical second chamber separated by asecond step. The dimensions of the first chamber may be selected tocorrespond with the exterior dimensions of the upper end of the blowseal housing, so that the base plate and the blow seal housing may bemounted together with the upper end in mating engagement with the firstchamber and bearing against a portion of the second step. The secondchamber is smaller in radius than the larger chamber, and is disposedproximate to and coaxially aligned with the smaller chamber and thelarger chamber. The base plate further defines a circumferential firstseal slot at the second chamber, and also defines a second low pressureair supply orifice, disposed through the base plate and communicatingwith the interior cavity third portion.

The top plate defines a plate opening, and has generally planar plateupper and lower surfaces. The plate opening is disposed above thesmaller chamber, the larger chamber, and the second chamber, with theplate lower surface proximate to the base plate.

A piston is provided and includes a piston first end, a piston secondend, and a generally cylindrical exterior surface having an exteriorsurface first portion disposed proximate to the piston first end withdiameter slightly smaller than the diameter defined by the smallerchamber of the blow seal housing. The exterior surface also has anexterior surface second portion defining a diameter slightly smallerthan the diameter defined by the larger chamber of the blow seal housingand disposed intermediate to the piston first and second ends, andfurther includes an exterior surface third portion defining a diameterslightly smaller than the diameter defined by the second chamber of thebase plate and disposed proximate to the piston second end. Acircumferential first shoulder is defined between the exterior surfacefirst and second portions, and a circumferential second shoulder isdefined between the exterior surface second and third portions. Theexterior surface second portion defines a circumferential second sealslot, and the exterior surface first portion defines circumferentialthird and fourth seal slots, respectively. The exterior surface thirdportion also defines a circumferential switch slot. The piston defines apiston passage extending therethrough. The piston passage includes apiston passage first portion separated from a larger piston passagesecond portion by a piston passage step, and a blow seal step disposedat the exterior surface third portion.

The piston is slidably disposed within the interior cavity second andthird portions, with the exterior surface first portion proximate to thesmaller chamber, the exterior surface second portion proximate to thelarger chamber, and the exterior surface third portion proximate to theplate opening. The piston is thus disposed partially within the interiorcavity second portion, the interior cavity third portion, and the plateopening, for sliding movement between a first,lowered position separatefrom the parison engagement assembly, and a second, raised position incontact with the parison engagement assembly. In the first, loweredposition, the piston is disposed so that the piston first end is incontact with the countersink of the blow manifold, the first shoulder isin contact with the step of the blow seal housing, and the piston secondend is generally flush with the plate upper surface. In the second,raised position, the second shoulder is in contact with the second stepand the piston second end is elevated, projecting above the plate uppersurface and in contact with the parison engagement assembly.

A flexible, resilient first O-ring seal is disposed in the first sealslot at the second chamber of the base plate, surrounding and bearingagainst the exterior surface third portion of the piston, making sealingcontact between the piston and the interior cavity third portion. Aflexible, resilient second O-ring seal is disposed in the second sealslot, surrounding the exterior surface second portion of the piston, andbearing against the blow seal housing at the larger chamber, makingsealing contact between the piston and the interior cavity secondportion. In addition, a flexible, resilient third O-ring seal isdisposed in the third seal slot, surrounding the exterior surface firstportion of the piston, and bearing against the blow seal housing at thesmaller chamber, and also making sealing contact between the piston andthe interior cavity second portion. The O-ring seals may be formed of aflexible, resilient polymeric material. A U-cup seal is disposed in thefourth seal slot, surrounding the exterior surface first portion of thepiston, and bearing against the blow seal housing at the smallerchamber.

Disposed within the piston passage second portion is a rod bearingretainer. A rod bearing chamber is defined through and within the rodbearing retainer and includes a rounded, circumferential interiorshoulder. The exterior dimensions of the rod bearing retainer arepreferably chosen to correspond with the dimensions of the pistonpassage second portion, so that the upper surface of the rod bearingretainer is flush with the blow seal step and the rod bearing retainerbears against the piston passage step. Disposed within the rod bearingchamber is a rod bearing. The dimensions of the rod bearing may beselected so that the rod bearing fits between the interior shoulder ofthe rod bearing retainer and the piston passage step. A blow seal isdisposed partially within the blow seal step, bearing against the rodbearing retainer. The blow seal, the rod bearing retainer and the rodbearing may be mounted to the piston using a snap ring disposed in acircumferential snap ring slot defined in the blow seal.

A heater is provided for thermal contact with the blow mold rod sealassembly, whereby heat may be introduced into the blow mold rod sealassembly so that a portion of the O-ring seals and the U-cup seal incontact with the blow mold rod seal assembly may be maintained at atemperature above a predetermined level. The predetermined level ischosen so that the O-ring seals and the U-cup seal maintained attemperatures above the predetermined level retain their sealingproperties and do not adhere to surfaces disposed in sliding contactwith the seals when a cryogenic fluid is utilized to cool plasticcontainers blow molded from parisons. The heater may include a pluralityof first heater elements for heating the blow manifold, with each firstheater element mounted at least partially within one of a plurality offirst heater element cavities defined in the blow manifold. The heaterfurther includes a plurality of second heater elements for heating thebase plate, each second heater element mounted at least partially withinone of a plurality of second heater element cavities defined in the baseplate. The first and second heater elements may be electrical resistanceheater elements connected to a source of electrical power. The firstheater elements provide heat energy to the blow manifold, and the secondheater elements provide heat energy to the base plate, whereby the blowseal housing, in thermal contact with the blow manifold and the baseplate, receives sufficient heat energy so that at least the outercircumferential portion of the second O-ring seal disposed in slidingand sealing contact with the blow seal housing at the larger chamber,and at least the outer circumferential portions of the third O-ring sealand the U-cup seal in sliding and sealing contact with the blow sealhousing at the smaller chamber are maintained at a temperature above thepredetermined level. In addition,the first heater elements providesufficient heat energy whereby at least the inner circumferentialportion of the first O-ring seal in sliding and sealing contact with thepiston at the exterior surface third portion is maintained at atemperature above the predetermined level.

A piston proximity switch is mounted to a switch mounting plate attachedto the base plate so as to be disposed within the plate opening andproximate to the piston. A seal extension housing is mounted below theblow manifold with a coupling extending partially within the blowmanifold stepped bore defined in the blow manifold and partially withina seal extension housing first stepped bore defined in a seal extensionhousing upper end. A seal extension bushing is disposed within a sealextension housing second stepped bore defined in a seal extensionhousing lower end, and the seal extension bushing and an extensionhousing U-cup seal are mounted to the seal extension housing with aU-cup retainer and U-cup retainer fasteners. A heater band is mountedsurrounding the seal extension housing at the seal extension housinglower end. The extension housing U-cup seal acts to prevent blow airprovided to the blow manifold from escaping through the seal extensionhousing.

A tubular stretching rod having a rod lower end including a threadedportion and a rod upper end is mounted to the blow mold rod sealassembly for vertical sliding movement through the U-cup retainer, theseal extension bushing, the seal extension housing, the coupling, theinterior cavity first portion, the piston passage, the rod bearingretainer, the rod bearing, the blow seal, and into the parisonengagement assembly. In this way, the stretching rod is disposed to moveinto and longitudinally stretch a parison coupled to the parisonengagement assembly, to facilitate stretch blow molding a parison into acontainer. Further, the stretching rod acts as a cryogenic fluid tubeand thus a cryogenic fluid inlet port at the rod lower end forconnection to a source of a cryogenic fluid, and further defines aplurality of cryogenic fluid outlet ports at the rod upper end, wherebya cryogenic fluid may be introduced within a container after stretchingand blowing.

The first and second heater elements provide heat to the blow manifold,the base plate, the blow seal housing, the piston and the rod bearing sothat portions of the stretching rod disposed within the blow manifold,the base plate, the blow seal housing, the piston and the rod bearingare maintained at a temperature above a preselected level, reducingaccumulation of water ice on such portions of the stretching rod thatmay result from sublimation of water vapor present in blow air. Theheater band provides heat to portions of the stretching rod proximate tothe seal extension housing lower end sufficient to maintain suchportions of the stretching rod at a temperature above the preselectedlevel, reducing accumulation of water ice on the stretching rod fromsublimation of water vapor present in ambient air.

Vertical movement of the stretching rod is accomplished using a rodlessair cylinder assembly including a cylinder support mounted to a mountingplate, and an air cylinder vertically movable with respect to thecylinder support using air supplied though a flow control orifice from asource of compressed air. A stretching rod tooling, having a stretchingrod tooling lower surface, is mounted to and beneath the blow manifold.A stop rod is mounted to the air cylinder, and a stretching rod bumperpad is mounted to the stop rod, for contact with the stretching rodtooling lower surface when the air cylinder moves vertically upward. Astretching rod switch mounting bracket is attached to the stretching rodtooling, and supports a cylinder proximity switch, which is electricallyconnected to the air cylinder assembly. The air cylinder assembly isalso electrically connected to the piston proximity switch.

The cylinder assembly may be coupled to a pair of stretching rods usinga stretching rod plate mounted to the air cylinder, with each stretchingrod for use with one of a pair of stretch blow molding stations. A braceis attached to the stretching rod plate and defines a brace aperturethrough which the check valve is mounted. A T-fitting is attached belowand in fluid connection with the check valve, and a pair of opposing,generally U-shaped tubes are connected to the T-fitting. Each U-shapedtube is fluidly connected to a stretching rod. Further, each stretchingrod is adjustably mounted to stretching rod plate with a tappedstretching rod adjustment bracket attached to stretching rod plate,whereby the threaded portion of each stretching rod is threadablyengaged with the stretching rod adjustment bracket. The check valve isfluidly connected to a supply tube through which cryogenic fluid, suchas liquid nitrogen, may be supplied to the present invention.

Vertical sliding movement of the piston within the blow seal housing,the base plate, and the top plate is controlled by the introduction oflow pressure air into the interior cavity second portion of the blowseal housing through the first low pressure air supply orifice, and intothe interior cavity third portion of the base plate through the secondlow pressure air supply orifice. In the first, lowered position, thepiston is disposed with the first shoulder in contact with the step ofthe blow seal housing, and an upper volume is defined within the largerchamber proximate to the upper end of the blow seal housing. With thepiston in the lowered position, the upper volume communicates with thesecond low pressure air supply orifice and the piston proximity switchis disposed in contact with the exterior surface third portion of thepiston, outside of the switch slot. In the second, raised position, thepiston is disposed with the second shoulder in contact with the secondstep of the base plate, and a lower volume is defined within the smallerchamber proximate to the lower end of the blow seal housing. With thepiston in the raised position, the lower volume communicates with thefirst low pressure air supply orifice and the piston proximity switch isdisposed in engagement with the switch slot.

In use, low pressure air supplied to the lower volume through the firstlow pressure air supply orifice raises the piston to the second, raisedposition, while supply of low pressure air to the upper volume throughthe second low pressure air supply orifice exerts downward pressure tomove the piston to the lowered position. The piston proximity switchacts to signal the position of the piston, indicating whether the pistonis in the lowered position or not in the lowered position. The first andsecond O-ring seals act to contain supplied air within the upper volume,and the second and third O-ring seals act to contain supplied air withinthe lower volume.

With the piston in the raised position, the piston proximity switchmoves into the switch slot and activates the air cylinder assembly,whereby the air cylinder moves vertically upward along the cylindersupport. Upward movement of the air cylinder is limited by contact ofthe stretching rod bumper pad with stretching rod tooling lower surface,triggering the cylinder proximity switch to stop movement of the aircylinder.

The stretching rod slides vertically upward through the U-cup retainer,the seal extension bushing, the seal extension housing, the coupling,the interior cavity first portion, the piston passage, the rod bearingretainer, the rod bearing, the blow seal, and the parison engagementassembly, and into the interior of a parison mounted to the parisonengagement assembly. By selecting the length of the stop rod, verticalmovement of the stretching rod into a parison may be selected to stretchthe parison to form a container of a desired size. In addition, fineadjustment of vertical sliding movement of the stretching rod may bemade by rotating and threadably advancing the stretching rod withrespect to the stretching rod adjustment bracket.

With the piston in the raised position, blow air may be supplied to thepresent invention, entering the blow manifold through the first andsecond blow air inlet ports, into the interior cavity first portion, andalso into the lower volume thereby providing additional upward pressureagainst the piston first end. The U-cup seal provides slidable, sealingcontact between the piston and the interior cavity second portion toprevent blow air from entering the larger chamber of blow seal housing.Due to upward pressure on the piston from blow air, the blow seal isurged upward against the parison engagement assembly with sufficientforce to form a seal permitting blow air to enter a parison engagedtherewith. Blow air flows through the interior cavity first portion ofthe blow manifold, external to the stretching rod, and into the pistonpassage, the rod bearing retainer, the rod bearing seal, and the blowseal, so that blow air may pass through the parison engagement assemblyfor blowing a parison into a container.

After stretching and blowing a parison into a container, high pressureblow air is released from the blow air outlet port so that blow air nolonger exerts upward pressure on the piston at the piston first end. Lowpressure air is then supplied to the upper volume through the second lowpressure air supply orifice, exerting downward pressure on the piston atthe second shoulder, causing the piston to move downward to the loweredposition.

After formation by stretching and blowing from a parison, a containerhas a relatively high temperature, and such containers may beadvantageously cooled by supplying a cryogenic fluid to the interior ofthe container, cooling and heat-setting the container from within. Thepresent invention provides for such cooling by introducing cryogenicfluid within a container through the supply tube, the check valve, theU-shaped tube, and into the stretching rod through the cryogenic fluidinlet port. Cryogenic fluid then emerges from the stretching rod at thecryogenic fluid outlet ports, within the container, and acts to quicklyquench and heat-set the container to permit rapid removal from the blowmold. The cryogenic fluid also cools the stretching rod, the piston, theblow manifold, the blow seal housing, and the base plate, along with theO-ring seals and the U-cup seal.

Cooling of the stretching rod to a temperature below the preselectedlevel may cause water ice to accumulate thereon, with water ice formingfrom sublimation of water vapor present in blow air flowing around thestretching rod and through the blow manifold, the piston, and the rodbearing. With continued accumulation of water ice, the stretching rodmay be prevented from sliding through the blow manifold, the piston,and/or the rod bearing. To prevent this undesirable cooling of thestretching rod, the first and second heater elements heat the blowmanifold, the base plate, the blow seal housing, the piston and the rodbearing so that portions of the stretching rod within the blow manifold,the base plate, the blow seal housing, the piston and the rod bearingare maintained at a temperature above the preselected level. Inaddition, the heater band is provided to reduce accumulation of waterice from ambient air on portions of the stretching rod proximate to theseal extension housing lower end which might prevent sliding movement ofthe stretching rod through the seal extension housing. The heater bandheats portions of the stretching rod to a temperature above thepreselected level, eliminating accumulation of water ice resulting fromsublimation of water vapor present in ambient air.

Cooling of the O-ring seals and the U-cup seal to a temperature below apredetermined level may cause seal failure and/or adhesion to surfacedisposed in sliding contact with the seals. To prevent cooling of thesliding contact surfaces of the O-ring seals and the U-cup seal, thefirst heater elements warm the blow manifold and the second heaterelements provide heat energy to the base plate, whereby the blow sealhousing is warmed so that at least the outer circumferential slidingcontact portions of the first and second O-ring seals and the U-cup sealare maintained at a temperature above the predetermined level.Correspondingly, the first heater elements also warm at least the innercircumferential sliding contact portion of the first O-ring seal to atemperature above the predetermined level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational section view of a cryogenic blow moldingapparatus representing the present invention with the piston depicted inthe lowered position, and the top plate, the cylinder support, and thesupply tube shown in fragmentary form.

FIG. 2 is an elevational section view of a cryogenic blow moldingapparatus representing the present invention with the piston depicted inthe raised position, and the top plate, the cylinder support, and thesupply tube shown in fragmentary form.

FIG. 3 is an enlarged detail partial section view of a cryogenic blowmolding apparatus representing the present invention with the pistondepicted in the lowered position.

FIG. 4 is an enlarged detail partial section view of a cryogenic blowmolding apparatus representing the present invention with the pistondepicted in the raised position.

FIG. 5 is a detail section view taken along line 5—5 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following portion of the specification, taken in conjunction withthe drawings, sets forth the preferred embodiments of the presentinvention. The embodiments of the invention disclosed herein are thebest mode contemplated for carrying out this invention in a commercialenvironment, although it should be recognized and understood thatvarious modifications can be accomplished within the parameters of thepresent invention.

Referring now to the drawings for a detailed description of the presentinvention, reference is first made to FIGS. 1-4, generally depictingapparatus 10 for use in stretch blow molding plastic parisons intocontainers. Apparatus 10 is contemplated for use in simultaneouslystretch blow molding a pair of parisons into a pair of containers usinga pair of essentially symmetric stretch blow molding stations. As aresult, without loss of generality or descriptiveness, the presentinvention will now be described with respect to only one of the pairstretch blow molding stations, with it understood that the other of thepair of stretch blow molding stations is thereby also described.Apparatus 10 is depicted proximate to parison engagement assembly 12 forengaging a parison for stretch blow molding within a blow mold, notshown. Apparatus 10 includes blow mold rod seal assembly 14 havingthermally conducting blow manifold 16, thermally conductive blow sealhousing 18, and thermally conductive base plate 20, mounted to top plate22 with first fasteners, not shown, so that blow seal housing 18 issandwiched between and in thermal contact with blow manifold 16 and baseplate 20. Additionally, base plate 20 may be attached to top plate 22with second fasteners 24.

Blow manifold 16 defines first stage blow air inlet port 25 forconnection to a source of blow air, not shown, through blow air fitting26, and further defines second stage blow air inlet port 27, depicted inphantom, for connection to the source of blow air. In addition, blowmanifold 16 also defines interior cavity first portion 28 disposed influid connection with first and second stage blow air inlet ports 25 and27, chamfered countersink 30 communicating with interior cavity firstportion 28, and blow air outlet port, not shown.

Blow seal housing 18 includes upper end 31 and chamfered lower end 32,with dimensions of lower end 32 selected so that blow seal housing 18may be disposed proximate to blow manifold 16 with lower end 32 inmating engagement with countersink 30 of blow manifold 16. Blow sealhousing 18 defines interior cavity second portion 34 having generallycylindrical smaller chamber 36 and coaxially disposed generallycylindrical larger chamber 38 separated from smaller chamber 36 by step40. As shown in phantom in FIGS. 3-4, blow seal housing 18 furtherdefines first low pressure air supply orifice 42, disposed through blowseal housing 18 and communicating with interior cavity second portion34. With blow seal housing 18 engaged with blow manifold 16, smallerchamber 36 is disposed proximate to interior cavity first portion 28.

Base plate 20 is disposed proximate to blow seal housing 18 and definesinterior cavity third portion 44 having generally cylindrical firstchamber 46 and generally cylindrical second chamber 48 separated bysecond step 49. The dimensions of first chamber 46 may be selected tocorrespond with the exterior dimensions of upper end 31 of blow sealhousing 18, whereby base plate 20 and blow seal housing 18 may bemounted together with upper end 31 in mating engagement with firstchamber 46 and bearing against a portion of second step 49. Secondchamber 48 is smaller in radius than larger chamber 38, and is disposedproximate to and coaxially aligned with smaller chamber 36 and largerchamber 38. Base plate 20 further defines circumferential first sealslot 50 at second chamber 48, and as illustrated in phantom in FIGS.3-4, defines second low pressure air supply orifice 51, disposed throughbase plate 20 and communicating with interior cavity third portion 44.

Top plate 22 defines plate opening 52, and has generally planar plateupper and lower surfaces 53 and 54, respectively. Plate opening 52 isdisposed above smaller chamber 36, larger chamber 38, and second chamber48, with plate lower surface 54 proximate to base plate 20.

Piston 56 is provided and includes piston first end 58, piston secondend 60, and generally cylindrical exterior surface 62. Exterior surface62 has exterior surface first portion 64 disposed proximate to pistonfirst end 58 and having diameter slightly smaller than the diameterdefined by smaller chamber 36 of blow seal housing 18. Exterior surface62 also has exterior surface second portion 66 defining a diameterslightly smaller than the diameter defined by larger chamber 38 of blowseal housing 18 and disposed intermediate to piston first and secondends 58 and 60, and further includes exterior surface third portion 68defining a diameter slightly smaller than the diameter defined by secondchamber 48 of base plate 20 and disposed proximate to piston second end60. Circumferential first shoulder 70 is defined between exteriorsurface first and second portions 64 and 66, and circumferential secondshoulder 72 is defined between exterior surface second and thirdportions 66 and 68. Exterior surface second portion 66 definescircumferential second seal slot 76, and exterior surface first portion64 defines circumferential third and fourth seal slots 78 and 80,respectively. Further, exterior surface third portion 68 definescircumferential switch slot 82. Piston 56 also defines piston passage 84extending therethrough. Piston passage 84 includes piston passage firstportion 86 separated from larger piston passage second portion 88 bypiston passage step 89, and blow seal step 90 disposed at exteriorsurface third portion 68.

As a result of these dimensions of exterior surface 62, piston 56 may beslidably disposed within interior cavity second and third portions 34and 44, with exterior surface first portion 64 proximate to smallerchamber 36, exterior surface second portion 66 proximate to largerchamber 38, and exterior surface third portion 68 proximate to plateopening 52. Piston 56 may thus be disposed partially within interiorcavity second portion 34, interior cavity third portion 44, and plateopening 52, for sliding movement between a first lowered positionseparate from parison engagement assembly 12 as shown in FIGS. 1 and 3,and a second raised position in contact with parison engagement assembly12 as shown in FIGS. 2 and 4. In the first lowered position, piston 56is disposed so that piston first end 58 is in contact with countersink30 of blow manifold 16, first shoulder 70 is in contact with step 40 ofblow seal housing 18, and piston second end 60 is generally flush withplate upper surface 53. In the second raised position, second shoulder72 is in contact with second step 49 and piston second end 60 iselevated, projecting above plate upper surface 53 and in contact withparison engagement assembly 12.

Referring to FIGS. 1-4, flexible, resilient first O-ring seal 96 isdisposed in first seal slot 50 at second chamber 48 of base plate 20,surrounding and bearing against exterior surface third portion 68 ofpiston 56, making sealing contact between piston 56 and interior cavitythird portion 44. Similarly, flexible, resilient second O-ring seal 98is disposed in second seal slot 76, surrounding exterior surface secondportion 66 of piston 56, and bearing against blow seal housing 18 atlarger chamber 38, making sealing contact between piston 56 and interiorcavity second portion 34. Further, flexible, resilient third O-ring seal100 is disposed in third seal slot 78, surrounding exterior surfacefirst portion 64 of piston 56, and bearing against blow seal housing 18at smaller chamber 36, and also making sealing contact between piston 56and interior cavity second portion 34. In a preferred embodiment, O-ringseals 96, 98, and 100 are formed of a flexible, resilient polymericmaterial. U-cup seal 102 is disposed in fourth seal slot 80, surroundingexterior surface first portion 64 of piston 56, and bearing against blowseal housing 18 at smaller chamber 36. Preferably, U-cup seal 102 isformed of a flexible, resilient polymeric material.

As depicted in FIGS. 1-4, disposed within piston passage second portion88 is rod bearing retainer 110. Rod bearing chamber 112 is definedthrough and within rod bearing retainer 110 and includes rounded,circumferential interior shoulder 114. The exterior dimensions of rodbearing retainer 110 are preferably chosen to correspond with thedimensions of piston passage second portion 88, so that upper surface116 of rod bearing retainer 110 is flush with blow seal step 90 and rodbearing retainer 110 bears against piston passage step 89. Disposedwithin rod bearing chamber 112 is rod bearing 120, preferably formed ofa plastic material such as Teflon. The dimensions of rod bearing 120 maybe selected so that rod bearing 120 fits between interior shoulder 114of rod bearing retainer 110 and piston passage step 89. Blow seal 124 isdisposed partially within blow seal step 90, bearing against rod bearingretainer 110. Blow seal 124, rod bearing retainer 110, and rod bearing120 may be mounted to piston 56 using snap ring 126 disposed incircumferential snap ring slot 128 defined in blow seal 124.

One central feature of the present invention is a heater provided forthermal contact with blow mold rod seal assembly 14, whereby heat may beintroduced into blow mold rod seal assembly 14 so that a portion of atleast one of O-ring seals 96, 98, 100 and U-cup seal 102 in contact withblow mold rod seal assembly 14 may be maintained at a temperature abovea predetermined level. The predetermined level is chosen so that O-ringseals 96, 98, and 100, and U-cup seal 102 maintained at temperaturesabove the predetermined level retain their sealing properties and do notadhere to surfaces disposed in sliding contact with the seals when, aswill be described, a cryogenic fluid is utilized to cool plasticcontainers blow molded from parisons. In a preferred embodiment, whereO-ring seals 96, 98, and 100 and U-cup seal 102 are formed of aflexible, polymeric material, the predetermined temperature may bechosen to be about 30° C.

As shown in FIGS. 1-4, the heater may include a plurality of firstheater elements 130 for heating blow manifold 16, with each first heaterelement 130 mounted at least partially within one of a plurality offirst heater element cavities 131 defined in blow manifold 16. Theheater further includes a plurality of second heater elements 132 forheating base plate 20, each second heater element 132 mounted at leastpartially within one of a plurality of second heater element cavities133 defined in base plate 20. In a preferred embodiment, first andsecond heater elements 130 and 132 may be chosen to be any of a varietyof electrical resistance heater elements, such as heater cartridge no.J1062 available from Watlow, Saint Louis, Mo., electrically connected toa source of electrical power, not shown. It will of course be understoodthat heater elements 130, 132 other than electrical resistance heaterelements may be used within the scope of the present invention,including heater elements utilizing conduction, convection, or radiationheating. First heater elements 130 provide heat energy to blow manifold16, and second heater elements 132 provide heat energy to base plate 20,whereby blow seal housing 18, in thermal contact with blow manifold 16and base plate 20, receives sufficient heat energy so that the outercircumferential portion of second O-ring seal 98 in sliding and sealingcontact with blow seal housing 18 at larger chamber 38, and outercircumferential portions of third O-ring seal 100 and U-cup seal 102 insliding and sealing contact with blow seal housing 18 at smaller chamber36 are maintained at a temperature above the predetermined level. Inaddition, first heater elements 130 provide sufficient heat energywhereby the inner circumferential portion of first O-ring seal 96 insliding and sealing contact with piston 56 at exterior surface thirdportion 68 is maintained at a temperature above the predetermined level.

Referring to FIGS. 1-4, piston proximity switch 134 is mounted to switchmounting plate 135, and switch mounting plate 135 is attached to baseplate 20 so that piston proximity switch 134 is disposed within plateopening 52 and proximate to piston 56. Seal extension housing 136 ismounted below blow manifold 16 using fasteners, not shown, with coupling138 extending partially within blow manifold stepped bore 140 defined inblow manifold 16 and partially within seal extension housing firststepped bore 142 defined in seal extension housing upper end 144. Sealextension bushing 146 is disposed within seal extension housing secondstepped bore 150 defined in seal extension housing lower end 152, andseal extension bushing 146 and extension housing U-cup seal 148 aremounted to seal extension housing 136 with U-cup retainer 154 and U-cupretainer fasteners 156. Heater band 158, such as Watlow no. MB1N1JN1, ismounted surrounding seal extension housing 136 at seal extension housinglower end 152. Extension housing U-cup seal 148 acts to prevent blow airprovided to blow manifold 16 from escaping through seal extensionhousing 136.

Tubular stretching rod 164 having rod lower end 166 including threadedportion 168 and rod upper end 170 is mounted to blow mold rod sealassembly 14 for vertical sliding movement through U-cup retainer 154,seal extension bushing 146, seal extension housing 136, coupling 138,interior cavity first portion 28, piston passage 84, rod bearingretainer 110, rod bearing 120, blow seal 124, and into parisonengagement assembly 12. In this way, stretching rod 164 is disposed tomove into and longitudinally stretch a parison coupled to parisonengagement assembly 12, to facilitate stretch blow molding a parisoninto a container in the well-known manner. Additionally, stretching rod164 acts as a cryogenic fluid tube, and thus defines cryogenic fluidinlet port 176 at rod lower end 166 for connection to a source of acryogenic fluid, not shown, and further defines a plurality of cryogenicfluid outlet ports 178 at rod upper end 170, whereby a cryogenic fluidmay be introduced within a container after stretching and blowing.

First and second heater elements 130 and 132 provide sufficient heatenergy to blow manifold 16, base plate 20, blow seal housing 18, piston56 and rod bearing 120 so that portions of stretching rod 164 disposedwithin blow manifold 16, base plate 20, blow seal housing 18, piston 56and rod bearing 120 are maintained at a temperature above a preselectedlevel, reducing accumulation of water ice on such portions of stretchingrod 164 resulting from sublimation of water vapor present in blow air.While it will be recognized that the preselected level may be as low asthe melting point of water ice, that is, about 0° C., in order tofacilitate more rapid melting and evaporation of water ice which mayaccumulate on stretching rod 164 during cyclic operation of apparatus10, the preselected level may preferably be chosen to be somewhathigher, for instance about 10° C. In addition, where rapid cycling ofapparatus 10 is desired, the preselected level may be chosen at a yethigher level, for instance about 30° C. Similarly, heater band 158provides sufficient heat energy to portions of stretching rod 164proximate to seal extension housing lower end 152 sufficient to maintainsuch portions of stretching rod 164 at a temperature above thepreselected level, reducing accumulation of water ice on such portionsof stretching rod 164 resulting from sublimation of water vapor presentin ambient air.

With reference to FIGS. 1-4, vertical movement of stretching rod 164 isaccomplished using rodless air cylinder assembly 180. Air cylinderassembly 180 includes cylinder support 182 mounted to mounting plate184, and air cylinder 186 vertically movable with respect is to cylindersupport 182 using air supplied though flow control orifice 188 from asource of compressed air, not shown. Preferably, air cylinder assembly180 may be selected to be of the rodless air cylinder type, such asrodless air cylinder no. BC2-20-SK20.000-HEO available from Tol-O-Matic,Inc., Hamel, Minn. Mounting plate 184 may be mounted to base plate 20using mounting plate fasteners 190. In addition, junction box 192 isattached to mounting plate 184 using junction box fastener 194.Stretching rod tooling 200, having stretching rod tooling lower surface202, is mounted to and beneath blow manifold 16. Stop rod 206 is mountedto air cylinder 186 using stop rod fastener 208, and stretching rodbumper pad 210 is mounted to stop rod 206 for contact with stretchingrod tooling lower surface 202 when air cylinder 186 moves verticallyupward. Stretching rod switch mounting bracket 214 is attached tostretching rod tooling 200, and supports cylinder proximity switch 216,which is electrically connected to air cylinder assembly 180 throughjunction box 192. Air cylinder assembly 180 is also electricallyconnected to piston proximity switch 134.

Referring to FIGS. 1, 2, and 5, air cylinder assembly 180 may be coupledto a pair of stretching rods 164 using generally inverted T-shapedstretching rod plate 220 mounted to air cylinder 186 using stretchingrod plate fasteners 222, with each stretching rod 164 for use with oneof a pair of stretch blow molding stations, as previously described.Brace 224 is attached to stretching rod plate 220 using brace fasteners226 and defines brace aperture 228 through which check valve 230 ismounted. T-fitting 234 is attached below and in fluid connection withcheck valve 230, and a pair of opposing, generally U-shaped tubes 236are connected to T-fitting 234. Each U-shaped tube 236 is fluidlyconnected to an elbow fitting 238, and each elbow fitting 238 is fluidlyconnected to a stretching rod 164. Each stretching rod 164 is adjustablymounted to stretching rod plate 220 with tapped stretching rodadjustment bracket 242 attached to stretching rod plate 220 usingadjustment bracket fasteners 244, whereby the threaded portion 168 ofeach stretching rod 164 is threadably engaged with stretching rodadjustment bracket 242. In addition, check valve 230 is fluidlyconnected to a pair of input elbow fittings 246, which are in turnfluidly connected to a supply tube 248. Cryogenic fluid, such as liquidnitrogen, is supplied to the present invention through supply tube 248from the source of cryogenic fluid.

Vertical sliding movement of piston 56 within blow seal housing 18, baseplate 18 and top plate 20 is controlled by the introduction of lowpressure air into interior cavity second portion 34 of blow seal housing18 through first low pressure air supply orifice 42, and into interiorcavity third portion 44 of base plate 20 through second low pressure airsupply orifice 51. In the first, lowered position depicted in FIGS. 1and 3, piston 56 is disposed with first shoulder 70 in contact with step40 of blow seal housing 18, and upper volume 249 is defined withinlarger chamber 38 proximate to upper end 31 of blow seal housing 18.With piston 56 in the lowered position, upper volume 249 communicateswith second low pressure air supply orifice 51 and piston proximityswitch 134 is disposed in contact with exterior surface third portion 68of piston 56, outside of switch slot 82. In the second, raised positionillustrated in FIGS. 2 and 4, piston 56 is disposed with second shoulder72 in contact with second step 49 of base plate 20, and a lower volume250 is defined within smaller chamber 36 proximate to lower end 32 ofblow seal housing 18. With piston 56 in the raised position, lowervolume 250 communicates with first low pressure air supply orifice 42and piston proximity switch 134 is disposed in engagement with switchslot 82.

In use, low pressure air supplied to lower volume 250 through first lowpressure air supply orifice 42 acts to raise piston 56 to the second,raised position, while supply of low pressure air to upper volume 249through second low pressure air supply orifice 51 exerts pressure tomove piston 56 to the lowered position. Piston proximity switch 134 actsto signal the position of piston 56, indicating whether piston 56 is inthe lowered position or not in the lowered position. Piston proximityswitch 134 may be selected to be any of a variety of electromechanicalproximity switches, such as 8 mm, 24 volt DC switch no. BES-516-384E4-C3available from Balluff, Florence, Ky.). First and second O-ring seals 96and 98 act to contain supplied air within upper volume 249, and secondand third O-ring seals act to contain supplied air within lower volume250.

With piston 56 in the raised position, piston proximity switch 134 movesinto switch slot 82 and activates air cylinder assembly 180, whereby aircylinder 186 moves vertically upward along cylinder support 182, to theposition depicted in FIGS. 1 and 2. Upward movement of air cylinder 186is limited by contact of stretching rod bumper pad 210 with stretchingrod tooling lower surface 202, triggering cylinder proximity switch 216to stop movement of air cylinder 186. Cylinder proximity switch 216 maybe selected to be any of a variety of available proximity switches, suchas the Balluff 8 mm, 24 volt DC switch no. BES-516-384-E4-C3.

Stretching rod 164 slides vertically upward through U-cup retainer 154,seal extension bushing 146, seal extension housing 136, coupling 138,interior cavity first portion 28, piston passage 84, rod bearingretainer 110, rod bearing 120, blow seal 124, and parison engagementassembly 12, and into the interior of a parison mounted to parisonengagement assembly 12. By appropriately selecting the length of stoprod 206, vertical movement of stretching rod 164 into a parison may beselected in order to stretch the parison to the extent needed to form acontainer of a desired size. In addition, fine adjustment of verticalsliding movement of stretching rod 164 may be made by rotating andthreadably advancing stretching rod 164 with respect to stretching rodadjustment bracket 242.

With piston 56 in the raised position depicted in FIGS. 2 and 4, blowair may be supplied to the present invention, entering blow manifold 16through first and second blow air inlet ports 25 and 27, into interiorcavity first portion 28, and also into lower volume 250 therebyproviding additional upward pressure against piston first end 58. U-cupseal 102 provides slidable, sealing contact between piston 56 andinterior cavity second portion 34 to prevent blow air from enteringlarger chamber 38 of blow seal housing 18. As a result of upwardpressure on piston 56 resulting from blow air, blow seal 124 is urgedupward against parison engagement assembly 12 with sufficient force toform a seal permitting blow air to enter a parison engaged therewith.Blow air flows through interior cavity first portion 28 of blow manifold16, external to stretching rod 164, and into piston passage 84, rodbearing retainer 110, rod bearing seal 120, and blow seal 124, whereuponblow air may pass through parison engagement assembly 12 for blowing aparison into a container.

After stretching and blowing a parison into a container, high pressureblow air is released from the blow air outlet port so that blow air nolonger exerts upward pressure on piston 56 at piston first end 58.Thereafter, low pressure air is supplied to upper volume 249 throughsecond low pressure air supply orifice 51, exerting downward pressure onpiston 56 at second shoulder 72, causing piston 56 to slide downward tothe lowered position.

Immediately after formation by stretching and blowing from a parison, acontainer achieves a relatively high temperature. As previouslydescribed, such recently formed containers may be advantageously cooledby supplying a cryogenic fluid to the interior of the container, to cooland heat-set the container from within. The present invention providesfor such cooling by introducing cryogenic fluid within a containerthrough supply tube 248, check valve 234, U-shaped tube 236 and intostretching rod 164 through cryogenic fluid inlet port 176. Cryogenicfluid then emerges from stretching rod 164 at cryogenic fluid outletports 178, within the container, and acts to quickly quench and heat-setthe container to permit rapid removal from the blow mold. Although useof cryogenic fluid to rapidly cool containers is advantageous, suchfluid also acts to cool stretching rod 164, piston 56, blow manifold 16,blow seal housing 18, and base plate 20, along with O-ring seals 96, 98,100 and U-cup seal 102.

Cooling of stretching rod 164 to a temperature below the preselectedlevel may cause water ice to accumulate on stretching rod 164, the waterice forming from sublimation of water vapor present in blow air flowingthrough blow manifold 16, piston 56, and rod bearing 120, and aroundstretching rod 164. Continued accumulation of water ice on stretchingrod 164 may prevent sliding movement of stretching rod 164 through blowmanifold 16, piston 56, and/or rod bearing 120. To prevent thisundesirable cooling of stretching rod 164, first heater elements 130 andsecond heater elements 132 heat blow manifold 16, base plate 20, blowseal housing 18, piston 56 and rod bearing 120 so that portions ofstretching rod 164 disposed within blow manifold 16, base plate 20, blowseal housing 18, piston 56 and rod bearing 120 are maintained at atemperature above the preselected level. Further heater band 158 reducesaccumulation of water ice from ambient air on portions of stretching rod164 proximate to seal extension housing lower end 152 which mightprevent sliding movement of stretching rod 164 through seal extensionhousing 136. Heater band 158 heats portions of stretching rod 164 to atemperature above the preselected level, reducing accumulation of waterice on such portions resulting from sublimation of water vapor presentin ambient air.

Cooling of O-ring seals 96, 98, 100 and U-cup seal 102 to a temperaturebelow a predetermined level may cause seal failure and/or adhesion tosurface disposed in sliding contact with the seals. To prevent coolingof the sliding contact surfaces of O-ring seals 96, 98, 100 and U-cupseal 102, first heater elements 130 warm blow manifold 16 and secondheater elements 132 provide heat energy to base plate 20, whereby blowseal housing 18 is warmed so that the outer circumferential portions offirst and second O-ring seals 98 and 100 and U-cup seal 102 in slidingcontact with low seal housing 18 are maintained at a temperature abovethe predetermined level. Correspondingly, first heater elements 130 alsowarm the inner circumferential portion of first O-ring seal 96 insliding contact with piston 56 to a temperature above the predeterminedlevel.

It will be recognized that in heating stretching rod 164 to apreselected level that is at least about 0° C., first and second heaterelements 130 and 132 may necessarily also heat O-ring seals 96, 98, 100and U-cup seal 102 to a predetermined level that is about 30° C.

The present invention having been described in its preferredembodiments, it is clear that the present invention is susceptible tonumerous modifications and embodiments within the ability of thoseskilled in the art and without the exercise of the inventive faculty.Accordingly, the scope of the present invention is defined as set forthby the scope of the following claims.

What is claimed is:
 1. In a method of stretch blow molding a plasticparison mounted to a parison engagement assembly into a containerwherein a blow mold rod seal assembly defining a blow air inlet port andan interior cavity disposed in fluid connection with the blow air inletport is connected to a source of blow air, the improvement comprising:stretching the parison by sliding a stretching rod through the interiorcavity and into the parison, the stretching rod including a coolingfluid tube defining a cooling fluid inlet port and a cooling fluidoutlet port; connecting the cooling fluid inlet port to a source of acooling fluid to introduce the cooling fluid within the containerthrough the cooling fluid outlet port; and heating the blow mold rodseal assembly to maintain at least a portion of the stretching rod at atemperature above a preselected level to prevent accumulation on atleast a portion of the stretching rod of water ice sublimated from watervapor present in the blow air.
 2. The method of stretch blow molding aplastic parison mounted to a parison engagement assembly into acontainer as recited in claim 1, wherein the step of heating the blowmold rod seal assembly includes electrically heating the blow mold rodseal assembly to maintain at least a portion of the stretching rod aboveabout 10° C.
 3. A method of stretch blow molding a plastic parisonmounted to a parison engagement assembly into a container, whichcomprises: connecting a blow mold rod seal assembly defining a blow airinlet port and an interior cavity to a source of blow air; stretchingthe parison by sliding a stretching rod through the interior cavity andinto the parison, the stretching rod including a cooling fluid tubedefining a cooling fluid inlet port and a cooling fluid outlet port;connecting the cooling fluid inlet port to a source of a cooling fluidto introduce the cooling fluid within the container through the coolingfluid outlet port; and heating the blow mold rod seal assembly tomaintain at least a portion of the stretching rod at a temperature abovea preselected level to prevent accumulation on at least a portion of thestretching rod of water ice sublimated from water vapor present in theblow air.
 4. The method of stretch blow molding a plastic parisonmounted to a parison engagement assembly into a container as recited inclaim 3, wherein the step of heating the blow mold rod seal assemblyincludes electrically heating the blow mold rod seal assembly tomaintain at least a portion of the at stretching rod above about 10° C.5. In a method of stretch blow molding a plastic, parison mounted to aparison engagement assembly into a container wherein a blow mold rodseal assembly defining a blow air inlet port and an interior cavitydisposed in fluid connection with the blow air inlet port is connectedto a source of blow air, a piston defining a passage therethrough isdisposed at least partially within the cavity for sliding movementbetween a first position separate from the parison engagement assemblyand a second position in contact with the parison engagement assembly,and at least one flexible, resilient polymeric seal is disposed betweenand in sealing contact with the piston and the interior cavity, theimprovement comprising: stretching the parison by sliding a stretchingrod through the interior cavity and the passage and into the parison,the stretching rod including a cooling fluid tube defining a coolingfluid inlet port and a cooling fluid outlet port; connecting the coolingfluid inlet port to a source of a cooling fluid to introduce the coolingfluid within the container through the cooling fluid outlet port; andheating the blow mold rod seal assembly to maintain at least a portionof the at least one seal in contact with the blow mold rod seal assemblyat a temperature above a predetermined level.
 6. The method of stretchblow molding a plastic parison mounted to a parison engagement assemblyinto a container as recited in claim 5, wherein the step of heating theblow mold rod seal assembly includes electrically heating the blow moldrod seal assembly to maintain at least a portion of the at least oneseal above about 30° C.
 7. A method of stretch blow molding a plasticparison mounted to a parison engagement assembly into a container, whichcomprises: connecting a blow mold rod seal assembly defining a blow airinlet port and an interior cavity to a source of blow air; slidinglydisposing a piston defining a passage therethrough at least partiallywithin the cavity for movement between a first position separate fromthe parison engagement assembly and a second position in contact withthe parison engagement assembly; disposing at least one flexibleresilient polymeric seal between and in sealing contact with the pistonand the interior cavity; stretching the parison by sliding a stretchingrod through the interior cavity and the passage and into the parison,the stretching rod including a cooling fluid tube defining a coolingfluid inlet port and a cooling fluid outlet port; connecting the coolingfluid inlet port to a source of a cooling fluid to introduce the coolingfluid within the container through the cooling fluid outlet port; andheating the blow mold rod seal assembly to maintain at least a portionof the at least one seal in contact with the blow mold rod seal assemblyat a temperature above a predetermined level.
 8. The method of stretchblow molding a plastic parison mounted to a parison engagement assemblyinto a container as recited in claim 7, wherein the step of heating theblow mold rod seal assembly includes electrically heating the blow moldrod seal assembly to maintain at least a portion of the at least oneseal above about 30° C.